Thin glass film may be manufactured by one of several techniques. The most common methods are with a fusion draw tower, where molten glass flows over two surfaces, joins over a line, and is drawn into a sheet, or with a re-draw process where a glass plate is heated and drawn into a sheet. Either of these processes can produce thin glass with thicknesses of 100 microns or less.
Many applications of films, including glass films, may require thin film coatings. These coatings are commonly applied using vacuum-based physical vapor deposition (including chemical vapor deposition, sputtering, and evaporative coating). Vacuum processes can be accomplished by either batch processes, such as where the sheets are all contained in a vacuum chamber or air-vacuum-air processes where the supply and wind up rolls are at atmospheric pressure.
While these coating methods are commonly used, they are also expensive. There are several coating methods where roll processing is not generally economically feasible. These include chemical vapor deposition (CVD), low pressure CVD, and atomic layer deposition (ALD). These processes are commonly used in sheet-based processes, where entire plates may be coated at one time.
Besides the above mentioned vacuum-based vapor deposition coating methods, an ambient, liquid-based coating method called layer-by-layer (LBL) self-assembly may also be used to provide coatings on film and glass. LBL coating is a self-limiting deposition process similar to ALD; however it is carried out at ambient temperature and pressure, usually from aqueous solutions or dispersions. Traditionally, LBL coating has been done in batch mode using automated dip or spray coaters on relatively small area substrates. LBL coating in a continuous roll-to-roll fashion via immersion coating has been described in US Pat. App. No. 2004/0157047 (Mehrabi et al.) and LBL coating via spray coating has been described in U.S. Pat. No. 8,234,998 (Krogman et al.). However, to coat multiple layers (e.g. 50 to 100 layers) using these techniques in one pass requires a large footprint for the coating line.
There is a need in the art for a method of coating sheets that provides high performance coatings at a low cost and at a high through-put.